A vehicle having an idling stop function and a deceleration regenerative function has been developed for the conservation of the global environment and the improvement in fuel consumption rate (fuel efficiency). This kind of vehicle is provided with a plurality of DC power supplies including a battery and a capacitor and a voltage conversion apparatus including a DC-DC converter. The voltage conversion apparatus raises or lowers a voltage from each of the DC power supplies and supplies the raised or lowered voltage to a load. The voltage conversion apparatus also stores regenerated power generated by a generator provided in the vehicle in, for example, the capacitor.
For example, in a voltage conversion apparatus of JP 2011-155791 A or a voltage conversion apparatus illustrated in FIG. 7 of JP 4835690 B1, a switch is disposed on a power path between a load (a narrow voltage range auxiliary machine) that requires protection so as to prevent a voltage supplied thereto from dropping and a battery. A power storage is connected to a power path between the load and the switch through a DC-DC converter. A generator, a starter motor, and other loads (an auxiliary machine and a wide voltage range auxiliary machine) are connected to a power path between the battery and the switch.
For example, when the generator generates regenerated power due to deceleration of the vehicle, the switch is turned on to drive the DC-DC converter and the regenerated power is stored in the power storage. When the generator generates no regenerated power when the vehicle is in a state other than idling stop, the switch is turned on to drive the DC-DC converter and the power storage is discharged. In this case, in JP 2011-155791 A, the power storage is discharged up to a voltage with which the DC-DC converter can operate and the power storage can continuously drive the load throughout a specified period in which the voltage of the battery instantaneously drops.
When an engine is restarted after idling stop of the vehicle, a large current flows through the starter motor by starting the starter motor and the voltage of the battery instantaneously drops. Thus, at this time, the switch is turned off to electrically separate the load and the power storage from the battery and the starter motor, and the power of the power storage is supplied to the load through the DC-DC converter. Accordingly, the load is continuously and stably driven with the power of the power storage.
The DC-DC converter of the voltage conversion apparatus includes, for example, a bidirectional voltage raising/lowering chopper circuit as disclosed in JP 2001-268900 A, JP 2001-292567 A, and JP 2005-295671 A. The bidirectional voltage raising/lowering chopper circuit includes two half bridge circuits and reactor. Each of the half bridge circuits includes two switching elements connected in series. One end of the reactor is connected between the switching elements of one of the half bridge circuits, and the other end of the reactor is connected between the switching elements of the other half bridge circuit.
A load connected to a voltage conversion apparatus may have a trouble in its operation when the voltage supplied thereto drops lower than a predetermined value. Thus, it is necessary to stably supply power to such a load.
In a voltage conversion apparatus to which a plurality of DC power supplies are connected, when one of the DC power supplies is intensively used, the life of this DC power supply is shortened. Thus, in order to increase the life of each of the DC power supplies, it is necessary to effectively use the power of each of the DC power supplies. When a battery and a capacitor are connected, as the plurality of DC power supplies, to the voltage conversion apparatus corresponding to the deceleration regenerative function, it is preferred to increase the opportunity of using regenerated power stored in the capacitor.